1. Field of the Invention
The present invention relates to an active material coating apparatus to form an active material layer on a substrate formed with an electrode plate of a rechargeable battery, and a coating method using the same.
2. Description of the Related Art
A rechargeable battery includes an electrode plate of which an active material layer is formed on a current collector. In the rechargeable battery, ions emitted from a positive active material layer are moved into a cathode active material layer and are stored during charging, and the ions stored in the cathode active material layer are again returned to the positive active material layer during discharging. It is preferred for these positive and negative active material layers to have a uniform thickness on the current collector to obtain a more uniform characteristic of the rechargeable battery. For this purpose, an active material coating apparatus is used.
As an example, the active material coating apparatus includes an upper die and a lower die forming an outlet slot, a spacer interposed between the upper die and the lower die, and a controller controlling a gap between the upper die and the lower die.
The active material coating apparatus outputs the active material in a slurry state through the outlet slot formed on a front end of the upper die and the lower die The active material is then coated on substrates that are separated by a minute interval and proceed at the front side of the outlet slot.
However, if the gap between the upper die and the lower die is uniformly maintained by the spacer and the controller, the active material coating apparatus may non-uniformly form the thickness of the active material layer coated on the substrate in the width direction. This may be the result of a limitation of the processing accuracy for the upper die and the lower die or as a result of a material property change of the active material slurry.
Also, the active material coating apparatus includes the spacers that are formed with the same material between the upper die and the lower die. The edge portion of the spacers at the both ends of the outlet slot is raised, which increases the thickness of the active material layer. This may result in more non-uniform thicknesses of the active material on both outer ends of the width of the substrate.
As described above, when the thickness of the active material layer formed on the substrate is non-uniform in the length direction, the electrode plate forms a portion having different performance in a unit cell. Also, when the thickness of the active material layer formed on the substrate is non-uniform in the width direction, a plurality of electrode plates forming a rechargeable battery may have different performances, and the performance uniformity of the battery may be deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.